There are presently known devices for automatically actuating a clutch arranged between the engine and transmission of a motor vehicle. Such clutchs may be actuated by a servo motor, for example a pneumatic servo motor. The servo is selectively supplied with either suction to cause the clutch to disengage, or with air at atmospheric pressure to cause the clutch to engage. While there are no particular requirements for disengaging the clutch, for example when the servo disengages the clutch by a supply of suction to the servo motor, the engagement of the clutch by a supply of atmospheric pressure air to the servo motor should be accurate and smooth enough to avoid any undue jolting or jerking of the vehicle.
In one known embodiment of an automatic vehicle clutch, the servo motor is employed only to actuate the clutch when the vehicle is in motion, that is, upon shifting manually from one speed to another. In this process, air is supplied to the servo motor faster or slower depending upon the accelerator position. In order to start the vehicle from a stationary position, however, a separate centrifugal clutch is employed.